Optical pickup device and optical disc apparatus
In the optical pickup device, while reflection light reflected from the optical multi-layer disc is divided into a plurality of regions so as to produce a plurality of divided optical beams, the divided optical beams are focused onto different positions on a photodetector, and a focus error signal is detected by employing a plurality of the divided optical beams by utilizing the knife edge method, and further, a tracking error signal is detected by employing a plurality of the divided optical beams. Furthermore, the dividing regions of the optical beam and light receiving parts are arranged in such a manner that stray light derived from other layers of the optical disc is not entered to a servo signal-purpose light receiving part of the photodetector when the divided optical beam is focused onto a target layer of the optical disc.
1. An optical pickup device comprising:
a semiconductor laser for emitting laser light;
an objective lens for irradiating luminous flux emitted from said semiconductor laser to an optical disc;
a diffraction grating for branching luminous flux reflected from the optical disc; and
a photodetector having a plurality of light receiving parts which receive luminous flux branched by said diffraction grating; wherein:
said diffraction grating has 3 sets of regions “A”,'“B”, and “C”;
among disc diffraction light diffracted by a track formed on said optical disc,
zero-order disc diffraction light is entered to said region “A” of the diffraction grating; and
the zero-order disc diffraction light, +first-order disc diffraction light, and −first-order disc diffraction light are entered to the region “B” thereof;
said photodetector detects a reproduction signal from grating diffraction light diffracted by said regions “A”, “B”, and “C”;
two, or more light receiving parts of said photodetector for detecting either +first-order grating diffraction light or −first-order grating diffraction light of said diffraction grating region “A” are arrayed in a substantially straight line along a direction which is made substantially coincident with a radial direction of said optical disc; and wherein:
two, or more light receiving parts of said photodetector for detecting either +first-order grating diffraction light or −first-order grating diffraction light of said diffraction grating region “B” are arrayed along a direction which is made substantially coincident with a tangential direction of said optical disc.
2. An optical pickup device as claimed in claim 1 wherein:
a focus error signal is detected based upon the −first-order grating diffraction light diffracted by the region “B” of said diffraction grating;
a tracking error signal is detected based upon the +first-order grating diffraction light diffracted by the regions “A” and “B” of said diffraction grating;
an offset correction signal for the tracking error signal is detected based upon the −first-order grating diffraction light diffracted by the region “A” of said diffraction grating; and
the reproduction signal is detected based upon a summation of the +first-order diffraction light diffracted by said regions “A”, “B”, and “C.”
3. An optical pickup device as claimed in claim 1 wherein:
the light receiving parts of said photodetector for detecting either the +first-order grating diffraction light or the −first-order grating diffraction light of the region “A” of said diffraction grating correspond to 4, or more light receiving parts.
4. An optical pickup device as claimed in claim 1 wherein:
the light receiving parts of said photodetector for detecting either the +first-order grating diffraction light or the −first-order grating diffraction light of the region “B” of said diffraction grating correspond to 4, or more light receiving parts.
5. An optical disc apparatus comprising:
the optical pickup device recited in claim 1 ;
a laser turning-ON circuit for driving said semiconductor laser employed in said optical pickup device;
a servo signal producing circuit for producing the focus error signal and the tracking error signal by employing the signals detected by said photodetector employed in said optical pickup device; and
an information signal reproducing circuit for reproducing an information signal recorded on the optical disc are mounted on said optical disc apparatus.
6. An optical pickup device comprising:
a semiconductor laser for emitting laser light;
an objective lens for irradiating luminous flux emitted from said semiconductor laser to an optical disc;
a diffraction grating for branching luminous flux reflected from the optical disc; and
a photodetector having a plurality of light receiving parts which receive luminous flux branched by said diffraction grating; wherein:
said diffraction grating has 3 sets of regions “A”, “B”, and “C”;
among disc diffraction light diffracted by a track formed on said optical disc,
zero-order disc diffraction light is entered to said region “A” of the diffraction grating; and
the zero-order disc diffraction light, +first-order disc diffraction light and −first-order disc diffraction light are entered to the region “B” thereof;
said photodetector detects a reproduction signal from luminous flux diffracted by said regions “A”, “B”, and “C”;
two, or more light receiving parts of said photodetector for detecting either +first-order grating diffraction light or −first-order grating diffraction light of said diffraction grating region “A” are arrayed along such a direction substantially perpendicular to a direction which is made substantially coincident with a radial direction of said optical disc;
two, or more light receiving parts of said photodetector for detecting either +first-order grating diffraction light or −first-order grating diffraction light of said diffraction grating region “B” are arrayed in a substantially straight line which is made substantially coincident with a tangential direction of said optical disc;
a quadrangle connected by both ends of a line segment “A” and both ends of a line segment “B” corresponds to a parallelogram, while said line segment “A” connects the respective light receiving parts for detecting the +first-order diffraction light of said diffraction grating region “A”, and said line segment “B” connects the respective light receiving parts for detecting the −first-order diffraction light of said diffraction grating region “A”; and wherein:
a line segment “C” which connects two, or more light receiving parts for detecting both the +first-order diffraction light and the −first-order diffraction light of said diffraction grating region “B” is equal to a distance between the line segment “A” and the line segment [[“B.”]] “B”.